Preparation of vinylidene fluoride

ABSTRACT

IN THE PYROLYSIS OF 1,1-DIFLUORO-1-CHLOROETHANE TO PRODUCE 1,1-DIFLUORO-ETHYLENE, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE PYROLYSIS ON THE PRESENCE OF WATER PREFERABLY THE REACTION IS EFFECTED IN A CORROSION RESISTANT REACTION TUBE FILLED WITH A CATALYTICALLY ACTIVE CARRIER MATERAL, THE RESIDUENCE TIME THEREIN RANGING FROM ABOUT 1 TO 15 SECONDS. THE AMOUNT OF WATER IS PREFERABLY ABOUT 20 TO 50 MOLE PERCENT THAT OF THE 1,1-DIFLUORO-1-CHLOROETHANE. THE PRESSURE MAY BE REDUCED AND THE TEMPERATURE IS PREFERABLY ABOUT 500 TO 650*C. IN THIS MANNER HIGH CONVERSIONS AND ALMOST QUANTITATIVE YIELDS ARE ACHIEVED.

United States Patent 3,830,856 PREPARATION OF VINYLIDENE FLUORIDE Johann Nikolaus Meussdoerfler, Blecher, and Hans Niederprum, Monheim, Rhineland, Germany, assignors to Bayer Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed Sept. 2, 1971, Ser. No. 177,443 Claims priority, application Germany, Sept. 8, 1970, P 20 44 370.3 Int. Cl. C07c 17/34 US. Cl. 260-653.5 7 Claims ABSTRACT OF THE DISCLOSURE In the pyrolysis of 1,1-difluoro-l-chloroethane to produce 1,1-difluoro-ethylen'e, the improvement which comprises eflecting the pyrolysis on the presence of water. Preferably the reaction is elfected in a corrosion-resistant reaction tube filled with a catalytically-active carrier material, the residence time therein ranging from about 1 to 15 seconds. The amount of water is preferably about 20 to 50 mole percent that of the 1,1-difluoro-1-chloroethane. The pressure may be reduced and the temperature is preferably about 500 to 650 C. In this manner high conversions and almost quantitative yields are achieved.

7 The present invention relates to a process for the preparation of vinylidene fluoride, CF =CH=, by selective pyroylsis of 1,1-difluoro-1-chloroethane.

It is known that a number of fluoro-olefins can be prepared from fluorinated alkanes containing other halogen atoms by removal of such other halogen atoms by means of metallic reducing agents in anhydrous polar solvents. this reaction, however, occurs only with great difliculty in the case of compounds with a difluorochloromethyl group and has, therefore, not become important for the industrial preparation of vinylidene fluoride from 1,1- difluoro-l-chloroethane (Houben Weyl, Methoden der Org. Chemie, 5/3, p. 377).

The reduction of fluorochloroalkanes by hydrogen for the preparation of vinylidene fluoride is known only from 1,1-difluoro-1,2-dichloroethane. This reaction is only possible on nickel catalysts at very high temperatures and results, owing to side reactions, only in small yields of vinylidene fluoride (US. Pat. No. 2,734,090).

Finally, the dehydrochlorination of 1,1-difluoro-1- chloroethane with bases has been described. This reaction also however has no industrial importance for the preparation of vinylidene fluoride because of the small conversions and yields. (Houben Weyl, Methoden der Org. Chemie, 5/3, p. 384).

At present, the most important process for the preparation of fiuorolefins and that most widely used on an industrial scale is the pyrolytic dehydrochlorination of the corresponding chlorofluoroalkane (DRP 761,526). Vinylidene fluoride is produced on pyrolysis of 1,1- difluoro-l-chloroethane, preferably carried out in the presence of catalysts such as nickel or copper, although the product is heavly contaminated with lay-products such as l-chloro-l-fluoroethylene (CFCl=CI-I and 1,1,1- trifluoroethane (CF -CH which are produced at the necessarily high temperature in side reactions by dehydrofluorination of the 1,l-difluoro-1-chloroethane and by further addition of the hydrogen fluoride formed to the vinylidene fluoride already produced (U.K. Pat. No. 823,998).

Considerable improvement of this reaction in regard to the yield of vinylidene fluoride was first achieved by the addition of chlorine to the 1,l-difluoro-l-chloroethane (German Auslegeschrift No. 1 253 702), but this process also has various disadvantages. Besides corrosion problems and the relatively low degree of reaction in the con- 3,830,856 Patented Aug. 20, 1974 "ice version of 1,1-difluoro-1-chlorethane to 1,1-difluoroethylene, even with very high residence times, the addition of chlorine produces considerable amounts of 1,l difluoro-Z-chloroethylene, which greatly interferes in the polymerization of vinylidene fluoride and is difficult to remove:

It is accordingly an object of the present invention to provide a process for producing vinylidene fluoride economically and in high yield.

This and other objects and advantages are realized in accordance with the present invention wherein there is provided a process for the preparation of 1,1-difluoroethylene by pyrolysis of 1,1-difluoro-l-chloroethane, optionally in the presence of a catalyst, characterized in that the 1,1-difluoro-1-chloroethane is pyrolyzed in the presence of water.

It was surprising to find that the pyrolysis of -1,1-difluoro-l-chloroethane to give excellent yields of vinylidene fluoride is possible in the presence of water without hydrolysis of the trihalomethyl groups which are normally very sensistive to water (Handbuch der Kaltetechnik, Vol. IV, Die Kaltemittel, Springer, 1956, pp. 373, 345 to 348).

Hitherto, a catalytic eifect of water has only been observed in the intermolecular dehydrochlorination of difluorochloromethane CF CIH to give tetrafluoroethylene CF =OF by pyrolysis (German Auslegeschrift 1,073,475):

(2) Reaction of vinylidene chloride with hydrofluoric acid:

CCl =CH +2HF- CF ClCH +HCl (3) Addition of hydrogen fluoride to acetylene to give 1,1-difluoroethane followed by chlorination to give 1,1- difluoro-l-chloroethane:

CHECH+2HF CF HCH CF HCH +Cl CF ClCH +HCl The vinylidene fluoride which can be prepared in accordance with the invention in high yields and in very pure form is an industrially important monomer which can be converted to interesting homoand co-polymers a less water is between about 0.5..and.- 75.,.preferably between about 20 and 50 mole percent. The reaction residence time. i.e. the time spent in the reactor, should be about 0.1 to 60,-preferably about 1 to l5,seconds. The reactor is preferably made of nickel but copper can also be used.. It has also proved to be advantageousforthe'reactor to contain fillers which increase the surface area and whichv are stable underthe reaction condition, such as nickel fillings, copper fillings, Raschig rings of resistant material such as Carborundurn, quartz or graphite, etc. By this means, thorough intermixing of stean1' and 1,l-difiuor-1- chloroethane isachieved and a more uniform temperature of the gas mixture over thecross-sectional area of the reaction tube is obtained owingto the better thermal conductivity properties; possible catalytic effects can also not be excluded.

The reactor can be heated externally to the required reaction temperatures of about 400 to 700 C., preferably about 500 to 650 C.; however direct heating with an oxyhydrogen flame is also possible, by which means the required amounts of steam are introduced at the same time. The reaction product is recovered in the usual way in that the aqueous hydrochloric acid is first removed, the residual gases are dried, freed from entrained hydrochloric acid by means of bases and then condensed. Unreacted 1,l-difiuoro-l-chloroethane can now, after separation, for example by fractional distillation, be recycled to the reactor and again subjected to pyrolysis.

The process according to the invention is illustrated below in greater detail by means of the following examples:

Example 1 123.5 g. (=1.2 mole of CF ClCI-I together with 7 g. of H 0 (=0.39 mole) were pyrolyzed for an hour at 550 C. in a nickel tube in which the residence time was 10 seconds. The composition of the product was as follows:

This corresponds to a conversion of about 48% CF ClCH of which 98% was converted to CF =CH Example 2 117 g. (=1.1 mole) of CF Cl-CH together with 6.7 g. (0.37 mole) of H 0 were pyrolyzed for an hour at a temperature of 600 C. and a residence time of 10 seconds in a copper reaction tube filled with nickel fillings. The reaction product had the following composition:

86.2% CF2=CH2 12.4% CF ClCH 1.0% crcizcu -....This corresponds to aconversion of the CF Cl-CH of about 88% of which 98% was converted to CFZZCH} Example 3 77.5 g. (0.77 mole) of CF ClCH together with 14 g. (0.77 mole) of'H O were pyrolyzed for an hour witha residence time of 10 seconds, and a temperature of600" C. in a nickel reaction tube filled with Carb'orundu'm Raschig rings. A product of the followingcomposition was obtained:

66.6% CF =CH .11 i

31.8% CF ClCH 0.4% CFCl=CH This correspondsto a conversion of 68.2% of which 97.7% was converted to CF' :CH

It will be appreciated that the instant specification and examples are set forth by way of illustration and not limitation and that various-modifications and changes may be made without departing from the spirit and scope of the present invention.

What is claimed is:

1. In the pyrolysis of l,l-difiuoro-l-chloroethane to produce 1,1-difluoro-ethylene, the improvement which comprises effecting the pyrolysis in the presence of about 0.5 to 75 mole percent at a temperature of about 400 to 700 C. of water.

2. The process of claim 1, wherein the pyrolysis is effected at a temperature of about 500 to 650 C.

3. The process of claim 1, wherein the pyrolysis is effected in the presence of about 20 to 50 mole percent of water.

4. The process of claim 1, wherein the pyrolysis is effected at reduced pressure.

5. The process of claim 1, wherein the residence time of the 1,l-difiuoro-l-chloroethane at pyrolysis temperature is about 0.1 to seconds.

6. The process of claim 1, wherein the residence time of the 1,l-difiuoro-l-chloroethane at pyrolysis temperature is about 1 to 15 seconds.

7. The process of claim 2, wherein the pyrolysis is effected at reduced presure in the presence of about 20 to 50 mole percent of water in a corrosion-resistant reaction tube filled with a material selected from the group consisting of nickel, copper, Carborundum, quartz and graphite, the residence time in said reaction tube ranging from about 1 to 15 seconds.

References Cited UNITED STATES PATENTS 2,551,573 5/l951 Downing et al. 260653.5 2,478,933 8/1949 Bratton et al. 260653.5 3,308,174 3/1967 Edwards et al. 260653.5

DANIEL D. HORWITZ, Primary Examiner 

